The present application relates generally to electronic and opto-electronic devices and a production method for the production of electronic and opto-electronic devices from an interpenetrating network configuration of nano structured high surface to volume ratio porous thin films with organic/inorganic metal, semiconductor or insulator material positioned within the interconnected void volume of the nano structure. The present application relates more specifically to lateral collection photovoltaic (LCP) structures.
Today, nanoparticles are proposed for, and used for, providing a high surface area to volume ratio material. Besides the large surface area they provide, nanoparticles can be embedded in organic/inorganic semiconductor/insulator materials (nano composite systems) to obtain a high interface area that can be exploited in, for example, the following optoelectronic and electronic applications: (a) charge separation functions for such applications as photovoltaics and detectors; (b) charge injection functions for such applications as light emitting devices; (c) charge storage functions for capacitors; and (d) ohmic contact-like functions for such applications as contacting molecular electronic structures.
There are difficulties with nanoparticles, however. These include their handling and, for electronic and opto-electronic uses, they also include the question of how to achieve electrical contact. In one approach for making optoelectronic devices from nanoparticle composite systems, isolated nanoparticles are diffused into a matrix of organic material. Each nanoparticle or nanoparticle surface must be electrically connected to the outside (by a set of electrodes) for electrical and opto-electronic function. This is achieved when the nanoparticles are arranged so that they are interconnected to the electrodes providing continuous electrical pathways to these particles. However, with the use of isolated nanoparticles, these particles will often fail to make good electrical contacts even if the volume fraction of nanoparticles is made close to unity.
Conventional photovoltaic operation uses some version of the basic horizontal structure seen in FIG. 1. Here light impinges on the horizontal layers and the resulting photogenerated electrons and holes, electrons and holes resulting from photogenerated excitons, or both are charge-separated with positive charge collected at the + charge-collecting electrode (anode) and negative charge collected at the − charge-collecting electrode (cathode), respectively. In the structure shown in FIG. 1, the device is composed of a p-type and an n-type solid semiconductor material, which semiconductor materials are functioning as the light absorbers, and as junction-formers creating the so-called built-in electric field providing the driving mechanism for charge separation. Other horizontal structures may use electron and hole affinity differences (band steps or band off-sets), with or without the built-in electric field mechanism, to drive charge separation. For photovoltaic action in FIG. 1, charge separation must result in electrons being collected at one electrode, the cathode, (bottom in FIG. 1) and holes being collected at the other electrode, the anode, (top in FIG. 1) giving rise to a current which can do external work (e.g., lighting a light bulb in FIG. 1).
Horizontal photovoltaic structures may be described in terms of two lengths: the absorption length, which is the distance light penetrates into the active (absorber) layer(s), e.g., the p-type and n-type layers shown in FIG. 1, before being effectively absorbed, and the collection length, which describes the distance in the active layer(s) over which photogenerated charge carriers can be separated and collected to the electrodes for use externally. In the case of photogeneration of excitons the collection length to be considered is usually the exciton diffusion length. The exciton diffusion length describes how far the excitons move by diffusion. The collection and the absorption lengths in horizontal structures such as the one shown in FIG. 1 are essentially parallel to one another. In these horizontal structures, the electrodes are usually solids although one or both can be electrolytes or some combination of electrolytes and solids. The electrodes can also be a porous solid structure or some combination of non-porous and porous materials.
The fact that the absorption and the collection lengths in the horizontal structure of FIG. 1 are essentially parallel means they are not independent. In horizontal structures such as that of FIG. 1, for effective photovoltaic operation, the appropriate collection length or lengths of the top active layer must be at least long enough to allow carriers generated by absorption in the top active layer to be collected and the appropriate collection length or lengths of the bottom active layer should be at least long enough to allow carriers generated by absorption in the bottom active layer to be collected and should be at least as long as the absorption length in that material for effective operation.
One alternative to the horizontal structure of FIG. 1 is a lateral collection approach that uses single crystal silicon structures using silicon (Si) wafer material. The Sliver® solar cell has been developed based on this concept. However, this lateral collection approach makes use of single crystal wafer silicon. The goal of the Sliver® approach is to use conventional silicon wafer-type material but, through the use of lateral collection, to reduce the amount of this expensive form of Si needed for the solar cell. In this process, single-crystal silicon is, for example, cut in 50 μm thick, 100 mm long, and 1 mm deep strips. The surrounding silicon holds these strips together. The Sliver® solar cell uses conventional silicon technology, but in a “slivered” configuration.
Intended advantages of the disclosed systems and/or methods presented herein teach configurations for the improvement of photovoltaic structures preferably fabricated from relatively low cost materials. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.